NASA is going back to the moon ó somehow, someway. The White House has ordered the agency to put American boots back on the lunar surface. The major unknowns at this point include the when, how, scale of the operation and cost. Also unclear is what exactly NASA would accomplish with such a mission and how it might affect plans for a human mission to Mars.NASA put 12 astronauts on the moon between 1969 and 1972. With the death last Friday of Apollo 16ís John Young, only five of those astronauts are still alive, and they range in age from 82 to 87. No human being has been beyond low Earth orbit since the end of the Apollo program.NASA acting administrator Robert Lightfoot told the Washington Post that the agency will partner with other countries in the return to the moon, but he did not say which ones. He said the moon plan will be a public-private partnership, but did not name any companies that might be involved. Details will emerge with the presidentís annual budget request to Congress, he said. He provided no specifics about the architecture of a moon program."We have no idea yet," Lightfoot said.PREVIOUS COVERAGE: Sen. Bill Nelson rips Trumpís NASA pickNASA is trying to do this without additional funding or a permanent administrator ó another top science position that hasnít been filled in the Trump administration. NASAís ongoing challenge in recent years has been reconciling the orders of politicians with the hard realities of flat budgets and the immutable laws of physics. This is the third time this century that NASA has been ordered to make a major shift in the focus of its human spaceflight program."Weíre always asked to change directions every time we get a new president, and that just causes you to do negative work, work that doesnít matter," former astronaut Scott Kelly, who spent nearly a year on the International Space Station in his last spaceflight mission, told the Post. "I just hope someday weíll have a president that will say, ĎYou know what, weíll just leave NASA on the course they are on, and see what NASA can achieve if we untie their hands.í"Scott Hubbard, former director of the NASA Ames Research Center, said he has heard grumbling in the space community about this latest change in NASA strategy. He said people are saying, "Please donít push the reset button again, because youíre just going to waste billions of dollars of previous investment."NASAís long-term human spaceflight strategy still includes a Mars mission in the 2030s, starting with a mission to orbit the planet and return home, followed by landing astronauts on Mars at an unspecified future date. Hubbard said thatís still doable ó "but not if NASA does a major re-pivot and goes all-in on a base on the moon. Then clearly Mars is pushed way off into the future."But Lori Garver, the NASA deputy administrator during President Barack Obamaís first term, said the people who donít want to see changes at NASA are "whiners." She has experience with implementing a major strategic shift, because after she and her fellow political appointees arrived at NASA headquarters in 2009, they upended the plans of George W. Bush for a return to the moon."This is a democracy," she said. "Elections matter."She noted that NASA is already building a jumbo rocket and crew capsule that could be used in a moon program. And she said NASA hasnít built anything yet thatís specifically designed for a Mars mission."Mars was more of a talking point," she said. "Itís out there as an aspirational goal."NASA is a $19 billion agency that does far more than just launch people into space. It spends roughly $5 billion a year on science missions, including robotic exploration of Mars and other planets. But the human spaceflight program has always been the heart of the agency and the foundation of its political support in Congress. The truism on the Hill has always been "No Buck Rogers, no bucks."Although the moon and Mars have some superficial similarities (craters, dust, rocks, mountains, no sign of life, etc.), they are quite different in the ideas of an aeronautical engineer. The moon has no atmosphere. Mars has a thin atmosphere that is devilish for spacecraft - itís too thin to be much help in braking a descending vehicle, but itís thick enough to cause overheating and turbulence.A flight to Mars would probably take the better part of a year and the round-trip mission would take more than two years. Astronauts would be exposed to radiation hazards and the psychological challenges of isolation in addition to the more obvious risks involved with trying to land safely on Mars and survive there.The triumph of the Apollo program came during the Cold War, when the race to the moon sent NASAís budget spiking. After Apollo, the agency shifted its focus to the development of the space shuttle, and later collaborated with other countries to build the International Space Station.After the Columbia space shuttle disintegrated during reentry in 2003, President George W. Bush ordered a major shift in NASA strategy. The shuttle fleet would be retired once the space station was complete. NASA would instead build new rockets and a new capsule with the goal of returning to the moon and eventually going to Mars. Thus was born the Constellation program.After President Barack Obama arrived in the White House, a presidential committee studied NASAís program and declared it was "on an unsustainable trajectory" due to a mismatch between ambitions and funding. Obama killed Constellation and ordered NASA to visit an asteroid, with Mars still the horizon goal. Obama also boosted funding for the "commercial crew" program, started by his predecessor, that would use privately owned rockets and capsules to ferry astronauts to orbit.PREVIOUS COVERAGE: Hereís how NASA is preparing to go to Mars When President Donald Trump took office, people in the space community expected a pivot back to the moon, restoring the Bush-era goal. The administration resurrected something called the National Space Council, with Vice President Mike Pence in charge. In October, Pence made a speech saying NASA would return to the moon. In December, President Trump made that goal the official U.S. space policy.NASA conceivably could attempt a limited mission to the moonís surface, akin to what the agency did with the Apollo program, but a mere "flags and footprints" mission could evoke opposition and derision from the been-there-done-that camp. NASA and its partners might instead attempt to create a permanently occupied research station similar to the ones in Antarctica.But the moon lacks certain things that Antarctica has in abundance ó not the least of which is air.While NASA tries to piece together a moon program, commercial space companies are gathering momentum and threatening to fly circles around the venerable U.S. space agency. Elon Musk and his start-up SpaceX are getting ready to fly a jumbo rocket called the Falcon Heavy, launching from the famed Pad 39A at the Kennedy Space Center, where Apollo 11 lifted off for the moon in 1969. Musk continues to promote his vision of putting people on Mars as soon as the next decade.Amazon founder Jeff Bezos has a space company, Blue Origin, which has emerged as a force in the commercial space world, with a suite of new rockets and ambitions to get involved in commercial lunar activity. Bezos has said he wants to see more people living and working in space. (Bezos owns the Washington Post.)SpaceX and Boeing, meanwhile, have contracts to launch NASA astronauts to the International Space Station. The first flights are scheduled for later this year. These are "commercial" contracts, meaning SpaceX and Boeing own their spaceships and rockets fully and are charging NASA a fee, as opposed to the traditional approach in which NASA owns all the hardware, and the companies have cost-plus contracts.This will end NASAís embarrassing reliance on the Russians for travel to and from the ISS. Since the shuttle fleet was retired, the United States has paid hundreds of millions of dollars a year for seats on Russiaís Soyuz spacecraft.At NASA headquarters, officials are awaiting the arrival of a permanent administrator. In September, President Trump nominated Rep. Jim Bridenstine, R-Okla., a member of the arch-conservative House Freedom Caucus, to be the NASA chief. The nomination drew criticism from the two Florida senators, Democrat Bill Nelson and Republican Marco Rubio, whose constituency includes a vast aerospace industry in and around NASAís Kennedy Space Center on Cape Canaveral. NASA has long enjoyed bipartisan support, and Bridenstineís critics said the top job shouldnít go to a politician. The full Senate has yet to vote on his nomination.Space policy experts said strong political leadership is essential when NASA wants to make a major change."The first year, which theoretically should be your strongest year, is gone," said Garver. "We were really off and running by this point."Proponents say another lunar mission will open up commercialization of the moon and set up further exploration to Mars and beyond. But the future of NASAís human spaceflight program will depend on money as much as on engineering prowess."If you only have a limited amount of money, maybe going to Mars is the better option rather than going back to the moon," Kelly said.He noted that NASA might save money if the mission to Mars was conceived as a one-way trip. But heís not volunteering for such a mission."Having lived on the space station for a year, I would not want to live the last days of my life on Mars," Kelly said.The Washington Postís Christian Davenport contributed to this report.